The following account of the prior art relates to one of the areas of application of the present application, hearing assistance devices, e.g. hearing aids.
A variety of sensors giving inputs about the current physical environment of a user is increasingly being used in hearing assistance devices. The ready availability of sensors to determine location movement and direction of a body has inspired to a lot of applications in handheld electronic devices in general. A few examples are given in the following.
EP1956867B1 describes the use of an ‘inclination-detector’ (e.g. gyroscope) to influence the setting of a preferred direction in a directional microphone system.
EP2116102B1 deals with a microphone system, wherein a compass or a gyroscope is used to determine a direction of head orientation of a user.
US2010278366A1 and US2010278365A1 deals with a hearing aid system, e.g. comprising a hearing aid and a handheld device, which are configured to communicate with each other, wherein the handheld device comprises a directional sensor (e.g. a gyroscope) to determine a ‘mode of operation’ of the system.
US2011293129A1 describes ‘head tracking’ (e.g. using a gyroscope).
U.S. Pat. No. 5,721,783 describes the use of a number of position determining sensors (incl. a gyroscope) in a remote control device for a hearing aid to determine the current location, etc., of the user.
Magnetic (inductive) wireless systems in hearing systems use one or more coils/antennas to transmit a signal from a hand-held or body-worn device to a hearing instrument. Typically dead-angles in the communication between the devices are experienced leading to drop-outs or reduced quality of the transmitted signal.
The transmission power could in principle be increased to reduce the problem. In practice, however, the available bandwidth and transmit power of a transmitted signal is limited due to regulation as well as technological challenges (large transmission power requires high voltage swings, potentially increasing IC costs (special processing) and leading to large (battery) power consumption).
The dead angles may alternatively be reduced by using two coils which simultaneously transmit the signal with one of the coils being phase-shifted 90 degrees (cf. e.g. US 2009/029646 A1). To completely remove the dead angles, a third coil is required, but this effectively halves the available data bandwidth, since the third coil cannot be used at the same time as the other two. It also adds (audio) latency to the system.
An alternative solution could be to measure the link quality in the auxiliary device in all three dimensions of a three dimensional antenna (e.g. 3 inductor coils having their winding axes oriented perpendicular to each other) when receiving data from a hearing assistance device, and to select a (received) signal for processing as the one having superior quality (e.g. the higher signal strength and/or the lower bit error rate). Such solution may, however, still exhibit drop-outs (especially when a relative movement between the head (hearing assistance device) and the auxiliary device is observed), since the decision to select a signal from a particular antenna is made based on ‘old information’, especially if a significant amount of the bandwidth is not to be eaten up by these link-quality packets'.